29. A common feature of thermal pollution and artificial eutrophication is that they both
a. ave sources that are idfficult to identify and control
b. cause large mats of algae to bloom in fresh water
c. are a result of power plants and other industrial activity
d. decrease the amount of oxygen dissolve din water

D

33. A true statement about greenhouse gases is that they
a. convert sunlight into heat energy that warms Earth
b. are concentrated in the stratosphere
c. trap heat that is radiated upward from Earth
d. are not affected by human activity

I don't think it's B or D. But I'm not sure what the correct answer is.

42. The critical difference between today's global warming and Earth's previous climate changes is that
a. human-made chemicals such as CFCs do not influence global warming
b. previous changes in climate were dramatic but very short-lived
c. scientists can now save all species from extinction by genetic engineering
d. global warming may occur much more rapidly than it did during previous climate changes due to rising carbon dioxide levels